Electrical resistivity mechanism in magnetorheological elastomer

Abstract

Magnetorheological elastomers (MRE) are smart materials made by aligning magnetic microparticles inside a liquid polymer. Once the polymer is cured, this anisotropic structure is kept, giving to the composite new properties such as a large change of electrical resistivity with applied pressure. In order to understand the conduction mechanism in such composite, the influence of pressure on the electrical resistivity of metal powders without polymer was first investigated. It was found that the initial resistivity of metal powder at zero pressure is about 10 8 Ω.cm for pure nickel powder and 10 6 Ω.cm for silver coated nickel particle. The piezoresistivity of the powders follows a power law with a coefficient close to (-1) at high compression, which allows to determine the thickness of the oxide layer. The change of resistance with pressure was found to be an order of magnitude larger for a MRE composite than for the same volume fraction of fillers dispersed randomly in the polymer. The filler particles have a high surface roughness, and when particles are brought into contact under pressure, the electric current takes place via microcontacts between asperities. The model of tunnel resistance developed in this study includes the roughness parameters and the thickness of the oxide layer found with the powder and introduces the thickness of the polymer layer as a new parameter. This model well reproduces experimental curves for piezoresistivity of composites informing on the thickness of the insulating polymer layer strongly adsorbed on the surface of particles.

Magnetorheological Elastomers and Their Applications

“…Following this research, a number of groups have reported the sensing capabilities of different MRE materials. Kchit and Bossis [30] found that the initial resistivity of metal powder at zero pressure is about 108 Ωcm for pure nickel powder and 106 Ωcm for silver coated nickel particles. The change in resistance with pressure was found to be an order of magnitude larger for a MRE composite than for the same volume fraction of fillers dispersed randomly in the polymer.…”

“…They used two kinds of magnetic particles: nickel and nickel coated with silver, dispersed in a silicone polymer as the polarised particles [30]. To understand the complex conductivity of particle embedded composites, quantitative or semi-quantitative models were developed by Zhao et al [34].…”

Kinetics of internal structures growth in magnetic suspensions

“…4. conductivity of chains of particles [14] the time needed to obtain a percolation between the opposite sides of the cell is the quantity of interest and it is worth noting that at time τ = 40000 the average chain length respective to the size of the box is l/h = 0.69 for h = 61 and l/h = 0.84 for h = 31. It means that, as expected intuitively, the percolation time decreases with the size of the box.…”

Composite Microdiscs with a Magnetic Belt: Preparation, Chaining Properties, and Use as Switchable Catalyst Carriers

“…5,6 These composites can be produced as microparticles with two notable properties. First, they can incorporate different functionalities having, for example, a magnetic core connected to a polymer shell with a catalytically active palladium group.…”